1. Field of the Invention
The present invention relates generally to a pre-chamber type diesel engines and more specifically to a transfer passage arrangement for such a diesel engine which obviates smoke formation due to combustion of fuel droplets in the main combustion chamber associated therewith.
2. Description of the Prior Art
FIG. 1 of the drawings shows a previously proposed combustion chamber arrangement 1 which includes a cavity 2 formed in the cylinder head 3 and a plug member 4 which closes the cavity to define a pre-chamber 5 into which fuel is injected by a fuel injector 6. The plug 4 is formed with a main transfer passage 7 which leads from the main combustion chamber 8 to the pre-chamber 5 so as to introduce the charge compessed in the main combustion chamber 8 into the pre-chamber in manner which causes it to assume a cyclonic swirling pattern therein.
In order to permit a fraction of the injected liquid fuel to pass from the pre-chamber 5 to the main combustion chamber 8 an auxiliary passage 9 is provided. This passage 9 permits an amount of relatively well atomized fuel escape from the pre-chamber 5 during the compression phase and thus reduce the amount of fuel involved in the initial spontaneous combustion which occurs therein upon the temperature and pressure of the charge reaching a sufficiently high level. This reduces the peak combustion temperature and the amount of NOx which tends to be formed.
To assist in the dispersion of the flame which is torched into the main combustion chamber 8 following the above mentioned spontaneous ignition of the rich charge in pre-chamber 5, and thus promote the combustion of the lean mixture present in the main combustion chamber, the crown of the piston 10 is provided with a so called "clover leaf" dispersion recess arrangement comprised of a elongate trench 11 and circular shallow dispersion sections 12 on either side thereof.
However, this arrangement has encountered the drawback that, in order to promote the desired amount of swirl in the pre-chamber 5, the main transfer passage 7 must be angled with respect to the pre-chamber so that the incomming charge enters the same essentially tangentially with respect the walls thereof, while in order to control the amount of liquid fuel which enters the main combustion chamber 8 the auxiliary transfer passage 9 is generally required to be angled with respect to the main one in manner which approaches 90 degrees. This disposition brings about the situation wherein the fuel droplets which pass through the auxiliary transfer passage 9 tend to impinge on the bottom of the trench 11 in a manner which induces the same to splash back up toward the cylinder head 3 and induces the situation wherein a faction of the same tends to escape beyond the bounds of the clover leaf recess and find its way into clearance H.
Under these circumstances, due to the relatively low exposure to the flame which is ejected from the pre-chamber and which is dispersed in the shaped recess in the piston crown, combustion of these fugitive droplets is slow promoting the formation of smoke.